The present invention relates generally to hypodermic injection devices, and is for use with needleless injectors in particular.
Needleless injectors are used as an alternative to hypodermic syringes for delivering liquid drugs and medicaments directly through the patient""s skin and into the tissues without using a needle. Such injectors consist of a piston pump, drive by a spring or gas, which ejects the drug through a small discharge orifice at sufficient rate and pressure to pierce the skin and enter the tissue through the hole thus formed.
In WO 95/03844, a needleless injector is disclosed which uses efficient energy storage and release means to provide a very compact and easy-to-use device, and the present invention is intended primarily for use with that device, although of course it could be adapted for use with alternative injectors. Ideally, a needleless injector would be provided to the end user pre-filled with the drug, self-powered, and ready for immediate use. The pre-filling of the injector would preferably be done by the drug manufacturer, thereby ensuring sterility, correct dose, and conformity to the approved specification.
However, whilst this is perfectly feasible for liquid-stable drugs such as heparin and some vaccines, for example, many drugs consist of two components, e.g. a lyophilised drug and its solvent. These drugs have a short shelf-life in liquid forms, and must be re-constituted and used immediately. Other drugs, which may be already in liquid form, are supplied in bulk to a pharmacy for example, and the pharmacist may be required to load the drug into the injector.
There is a long-standing requirement for a single dose disposable needleless injector which may be externally filled, and many inventions aim to provide external loading methodsxe2x80x94e.g. WO89/08469 (Parsons). Most such devices are complicated and costly, and are inconvenient to use. With the present trend towards single use disposable needleless injectors, the filling device ought to be very simple to use, and sufficiently inexpensive so that it may be disposed of with the injector.
Another invention, by Lindmayer, U.S. Pat. No. 4,518,385, is for a disposable syringe which is filled by the user in a conventional manner. After filling, the hollow filling needle is removed or broken off, and the syringe body is inserted into the power unit. The syringe body becomes the needleless dispensing member, and thus the syringe has a dual function. Although U.S. Pat. No. 4,518,385 does go some way in simplifying the loading process, there is still a substantial requirement for the user to exercise skill and judgement in using the device. Moreover, the syringe is intended for use with a multiple use power unit or actuator, which is complex and expensive.
The present invention seeks to overcome the limitations of prior art injectors, and provides a simple adaptor for use with a standard hypodermic syringe, which adaptor may be removed after filling the injector together with the syringe. After use, the adaptor covers the end of the needle to prevent or reduce likelihood of pricking the user.
Thus, according to a first aspect of the invention there is provided an adaptor for enabling a fluid to be introduced from an outlet of a filling device into an orifice of a needleless injector cartridge, comprising a first portion for engagement with the cartridge, and a device-engaging second portion for engagement with the filling device, whereby to maintain the outlet of the filling device in fluid communication with the orifice of the cartridge, the said first and second portions being connected to one another by a detachable connection.
According to a second aspect of the invention there is provided a needleless injector cartridge in combination with an adaptor for enabling a fluid to be introduced from an outlet of a filling device into an orifice of the cartridge, wherein the adaptor comprises a device-engaging portion whereby to maintain the outlet of the filling device in fluid communication with the orifice of the cartridge, the said first and second portions being connected to one another by a detachable connection.
With the syringe assembled to the needleless injector, the injectate may be transferred into the cartridge from the syringe, through the discharge orifice in the cartridge, thus to displace the cartridge piston by hydraulic pressure. Stop means is preferably provided to limit the displacement of the piston, so that the amount of injectate transferred into the injector cartridge is predetermined.
Another aspect of the invention is to provide for the reconstitution of a lyophilised drug. In a preferred embodiment, the lyophilised drug is stored in the drug cartridge between the discharge orifice and piston, so that the introduction of a liquid solvent through the orifice will dissolve the lyophilised drug and displace the piston by hydraulic pressure to a pre-determined stop.
The connection between the syringe guide and drug cartridge or cartridge retainer is preferably provided by a frangible joint or other detachable connection. After transferring the injectate, the syringe is given a sharp sideways pull which causes the guide to break away from the cartridge or its retainer at the frangible joint. Preferably the needle is protected by remaining inside the resilient seal, which itself remains attached to the syringe guide.
The invention in its various aspects is capable of providing a very safe, simple and convenient means of filling a pre-assembled, self-powered needleless injector to a pre-determined volume, with safe disposal of the filling syringe thereafter. The safety aspect is enhanced if the hypodermic syringe needle is blunt.